VLA Legacy Survey of Molecular Gas in Massive Star-forming Galaxies at High Redshift

Abstract

We present initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO(J = 1-0) transition in a sample of 30 submillimeter-selected, dusty star-forming galaxies at z = 2-5 with existing mid-J CO detections from ALMA and NOEMA, of which 17 have been fully observed. We detect CO(1-0) emission in 11 targets, along with three tentative (∼1.5-2σ) detections; three galaxies are undetected. Our results yield total molecular gas masses of 6-23×10 10 (α CO /1) M , with gas mass fractions, f gas =M mol /(M * +M mol ), of 0.1-0.8 and a median depletion time of (140±70) Myr. We find median CO excitation ratios of r 31 = 0.75±0.39 and r 41 = 0.63±0.44, with a significant scatter. We find no significant correlation between the excitation ratio and a number of key parameters such as redshift, CO(1-0) line width or Σ SFR . We only find a tentative positive correlation between r 41 and the star-forming efficiency, but we are limited by our small sample size. Finally, we compare our results to predictions from the SHARK semi-analytical model, finding a good agreement between the molecular gas masses, depletion times and gas fractions of our sources and their SHARK counterparts. Our results highlight the heterogeneous nature of the most massive star-forming galaxies at high-redshift, and the importance of CO(1-0) observations to robustly constrain their total molecular gas content and ISM properties.